DC-DC charger ground question

[ntsqd]

I don't have or need one with my current vintage of rigs, but I was pondering a question that came up about integrating solar with one.

Do DC-DC chargers float their ground or are they common to chassis ground?

What lead to this question was pondering how to get the solar to also charge the starting batteries. So far in my thinking I'm at needing at least three and maybe four high current / low voltage drop wires along with one or two DC-DC chargers. If only one then an older single-sense type ACR/VSR would be needed for the solar to truck battery isolation/connection.

If they are common then that's down to three such wires or cables. Which is still a heavy price to pay for that functionality. There has to be a better way that I've not figured out.

 

[rando]

I am not sure I understand the question completely - but an isolated DC-DC converter has two separate negative terminals (not really ground) that are electrically isolated from each other (at least in a DC sense), but they can be connected by the user. The non-isolated version has a single electrical negative terminal (but usually two connection points). It is up to the user to decide whether these are connected to the vehicle ground, but in almost all automotive applications they are.

 

[ntsqd]

The DC-DC charger's input negative would always be common to chassis ground. I guess what I'm asking is if the output negative is always connected to the input negative regardless of the DC-DC charger's status. If it is then the output negative is always common to chassis ground. If it is not then it is likely floating and not common to the chassis.
Common simplifys things considerably. Floating does not simplify anything.

 

[rando]

At least on Victron DC-DC converters, the input and output negative terminals are common on the non-isolated version, and are isolated on the isolated version, but you can tie them together if that is what you prefer.

 

[Jon R]

The Victron Orion Tr Smart 12/12-30 non-isolated has only three dc connection terminals - two positives and one negative.

In the isolated version (which I have) there are four terminals and the negatives are isolated regardless of the charger mode unless you tie them together in your wiring.

 

[ntsqd]

Thank you both!

 

[Jon R]

I think one of the reasons an isolated charger can be desirable in certain situations is corrosion prevention by avoiding a ground loop.

I bought an isolated charger prior to actually taking delivery of my Four wheel camper because discussions here led me to believe that the attachment of my camper to the truck would tie the truck structure and camper frame together electrically, and I didn’t want ground loop issues. It turned out the attachment does not electrically connect the camper to the truck. My camper also was delivered with a ground wiring error that tied the marker lights ground inside a wall to another ground. The easiest thing to do to get the lights working properly was to tie the ground systems together.